ATK Core Return Process
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NOTE:

• Core return can be any Small Block Chevy 350ci engine, except 1992-1997 LT1 style engines

Engine Specifications:

• Horsepower: 390
• Torque: 420
• Block: 1996-2000 OE roller block 4-bolt main 1-piece seal
• Bore/Stroke: 4.040 in. x 3.480 in.
• Displacement: 350 ci
• Crankshaft: OE Reground external balance rear of the crank/internal balance front of the crank
• Rods: OE powder metal 5.700 in.
• Pistons: Hypereutectic 10:1 Compression
• Rings: Moly
• Camshaft: Hyd. Roller
• Cam Specs: 220/224 @ 50 .528in/.536ex 110 LSA
• Timing Chain: Double Roller
• Cylinder Heads: ATK High-Performance aluminum with 2.020 in. /1.600 ex. valves
• Rocker Arms: Billet aluminum roller rockers 1.6 ratio
• Oil Pan: Rear sump 5qt (not for Chevelles with steering behind crossmember, some Corvettes, and 1962-2967 Chevy II’s)
• Oil Pump: Melling STD Volume
• Flexplate/Flywheel: Externally Balanced – Pioneer #FRA-159
• Balancer: Internally Balanced – PowerBond #PB1046-N
• Intake Manifold: ATK dual plane intake
• Distributor: HEI (Iron Gear)
• Water Pump: OE long pump

Recommended Components:

• Carburetor: Quick Fuel 680CFM Vacuum secondary’s electric choke #HR-680
• Fuel Pump: Holley mechanical 110GPH #12-327-11
• Spark Plugs: Autolite #3923
• Spark Plug Wires: 8 mm

Engine Info:

• Oil: Conventional / Non Synthetic 10W30
• Oil Filter: Wix or K&N
• Timing: 34-36 Degrees
• Spark Plug Gap: .035 in.
• Firing Order: 18436572
• Octane: 91+
• Stall Converter: 2200-2800
• Exhaust: 1 5/8 in. Headers

Disclaimer: The parts listed are ATK’s recommendations of parts to be used to obtain our power figures listed. Power figures can vary based on parts used by the end-user. It is the customer’s responsibility to verify components will work in their application. Some modifications to the vehicle may be required using these and or other aftermarket parts. . ATK reserves the right to substitute parts used in engines if necessary.

Engine Break-In Procedure

Use or break-in oil or conventional (non-synthetic) 10w30 oil with zinc additive for the first 500 miles of operation.  Do not drive for long periods at any single speed, always vary your speed. Do not tow a trailer or put other heavy loads on the vehicle. It is best to avoid long periods of idling during this period. Check the engine oil and coolant levels daily. 

Engines with flat tappet hydraulic cams only - Run the engine between 2,000 and 2,500 RPM's, with no-load on the engine for the first 30 minutes. Let the engine cool down completely and repeat process 2-3 more times. Do not idle the engine for any extended period at this time, this is critical to break in the camshaft.

At 500 Miles change the engine oil and filter using conventional (non-synthetic) oil with a zinc additive. Check fuel and ignition settings, adjust valves (where applicable).  Drive the next 500 miles normally, without high RPM's (below 5000 RPM), hard use, or extended periods of high loading or long periods of idling.

Change the oil and oil filter again at 1,000 miles. Continue using conventional (non-synthetic) oils and zinc additive, until about 4,000 miles. At that point, you may run a quality 10w30 synthetic oil if you choose. Use of oil with zinc or a zinc additive for the life of your engine is recommended.

Emissions Note:

This part is only legal for sale and use on Uncontrolled (Non-Emissions Controlled) Vehicles or on vehicles used solely for the purposes of closed competition racing.

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